The present invention relates to a method for raising the pH in acidic soils, especially in soils having a pH in the aluminum buffer range, i.e. less than 4.2. The aluminum buffer range is the pH range in which aluminum from the weathering of clay minerals, which is present as oxide or hydroxide, i.e. in nonionic form, at higher pH, passes into cationic solution.
To raise the pH such soils have hitherto been treated with lime, for example by sprinkling on or mixing into the soil. Existing stands were limed with about 3 t per ha every five years to stop further acidification. In the case of first afforestations, the recommended liming quantities are appreciably higher, up to 15 t per ha, depending on soil acidification, because of the higher acid sensitivity of the young plants. Since, owing to the now appreciably decreased acid emissions, significant further acidification of soils is no longer likely, liming will in future no longer have such immense importance in the case of mature stands. However, the mortality problem of afforestations on problem sites will continue, since the acid in the soils is not so quickly neutralized.
Attempts have been made to improve soil quality by mixing alkaline sandy and loamy soils with poly(meth)acrylates (Arid-Soil-Research-and-Rehabilitation, 1996, 10; 3, 277-285). The pH was observed to rise. This effect of pH being raised, which is actually undesirable in alkaline soils, can be explained by the bonding of protons to the acrylate, releasing metal cations, such as potassium, from the acrylate.
The situation is different in acidic soils. Soil suspensions in pure water have a pH some 0.6 units higher than a suspension in CaCl2 solution. This is because, in such soils, the exchange sites on the clay-humus complex are mostly occupied by protons and cationic acids and the pH of the soil solution is very slow to become established, i.e. equilibration is very slow between the clay-humus complexes of the soil and the soil solution (see: xe2x80x9cBodenxc3x6kologiexe2x80x9d, Georg Thieme Verlag Stuttgart 1997, p. 125). On adding KCl or CaCl2 to a soil suspension, the counterions on the exchanger complex are immediately released and the pH correspondingly lowered.
When the method of the invention is used to add poly(meth)acrylates to an acidic soil, the protons in the soil solution are trapped by the negatively charged carboxyl groups of the poly(meth)acrylates, so that a higher pH becomes established in the soil solution. This effect persists for a prolonged period, surprisingly for a period of many months. This could not be foreseen by one skilled in the art and permits a long-term raising of the pH of acidic soils.